Apparatus for and methods of controlling radar contact

ABSTRACT

Apparatus for and method of using derived information about the direction of propagation of an incoming radar beam to control radar return. The information about the direction of propagation of the incoming radar beam is used to alter aspects of a platform&#39;s orientation to control the cross section presented to the radar.

FIELD

The present disclosure relates to devices and methods for controllingradar contact between a platform such as an aircraft and a radar source.

BACKGROUND

There may be circumstances in which it is desirable to control contactthat a platform such as an aircraft (fixed wing, helicopter,multi-rotor-copter), watercraft, or land-based vehicle has with a radarsource. The use of “aircraft” or “platform” is intended herein toinclude all of these platforms and any platform whose radar signaturecould be controlled in response to the angle-of-arrival (AoA) of a radarsignal. The amount of radar contact may be regarded as the radarsignature of a platform as seen by a radar system. A platform's “radarsignature” includes the reflected energy's amplitude and polarization,and may also include features such as the Doppler shift due to thedistance between the radar and the platform changing over time and otherDoppler features such as spectral terms caused by the aircraft bodyrotating relative to the angle-of-arrival (AoA) of the radar beam, orcaused by vibrations or rotating propellers or turbines. A platform's“RCS parameters” capture its radar signature as a function of the AoA,frequency, and polarization of an incoming signal. As used herein, theterm “radar parameters” includes at least the radar's frequency and mayalso include items such as polarization, sweep-rate, modulation type(such as pulsed, or chirp) and bandwidth.

Various measures have been employed in the past to reduce a platform'sRCS such as shaping and the use of special materials to absorb the radarsignal so that less can propagate back to its source. Such measures,however, have limited effectiveness, and cannot be quickly controlled.Various measures have also been employed in the past to enhance the RCSsuch as adding corner reflectors or repeaters to reflect more of theradar signal so more can propagate back to its source. Such measures arecumbersome as they require additional physical space, complexity, andwork only in small sectors. It would be desirable to have real-timeadaptable “radar signature management objectives” The use of “radarsignature management objectives” as used herein refers to a set ofobjectives whereby one objective may be to reduce the platform'sobservability to some radars, another objective may be to increase theplatform's observability to other radars, and where the objectives areprioritized and the priority might be based on the radar's “beamparameters” or “radar parameters”. “Beam parameters” as used hereinrefers to one or more parameter such as the radar beam's AoA, frequency,polarization, and potentially other parameters such as magnitude,sweep-rate, and modulation type and bandwidth.

Platforms are sometimes configured with the ability to monitor theirorientation and course parameters. “Orientation parameters” as usedherein includes one or more parameters such as yaw, pitch and roll aswell as their derivatives (e.g. rate of change of an orientation angle).“Course parameters” as used herein includes parameters related toposition, including cartesian x, y, z coordinates or geospatiallatitude, longitude, and altitude coordinates. “Course” also refers tothe platform's track, the time series of its positions and theirderivatives including velocity-vector (rate of change in x, y, z) andacceleration. The ability to monitor orientation and course parametersis provided by many different means including compasses, gyros, opticaltrackers, inertial navigation systems (INS), inertial measurement units(IMU), satellite based systems such as the Global Positioning Systems(GPS) and the Global Navigation Satellite System (GLONASS) or similarly,triangulating on other incoming signals using direction finding or timedifference of arrival techniques.

Platforms are also configured with physical control mechanisms.“Physical control mechanisms” as used herein includes one or morerudders, ailerons, flaps, actuators that move thruster orientations,steering wheels and linkages or actuators that reorient therotation-axis of wheels, actuators that move throttles, actuators thatmove shiftable gears, actuators that apply brakes, or actuators thatdirectly move or rotate the platform, all of which are used to controlthe course parameters of the platform.

These platforms are often configured with a steering module configured(1) to have access to and the platform's course parameters andorientation parameters, (2) to access steering, and (3) to control thephysical control mechanisms so as to affect the platform's orientationparameters and course parameters based on the combination of steeringobjectives. “Steering objectives” as used herein includes all or somesubset of objectives regarding imposing a set of constraints and desireson how the platform's course parameters should be changed over thecourse of the flight, for purposes of (a) comfort, (b) safety, and (c)navigation, for example such as to simultaneously or separately (a) havethe apparent gravity always toward the bottom of the platform, (b) limitcontrol surface angles to avoid events like such as stalls and skids,and (c) obey a user's input, such as a pilot moving a control stick totell the steering module to make a turn and how sharp to make it, or thepilot instructing the steering module to guide the platform to adestination or waypoint and later changing the location of thedestination or waypoint.

These steering modules have been highly refined to simultaneously meetmultiple steering objectives. These steering modules do not, however,have the ability to manage or control a radar signature observed by anyparticular radar. Moreover, these steering modules do not have theinformation required to regulate a platform's radar signature presentedto a particular radar, such as access to the platform's RCS parameters,or access to the observing radar's beam parameters of an incoming radarsignal. “. Neither do these steering modules contemplate the existenceof an RCS, nor that an RCS observed by radar could be managed bychanging the platform's course parameters during a flight.

It is in this context of the need for the devices and methods disclosedin this application arise.

SUMMARY

The following presents a simplified summary of one or more embodimentsin order to provide a basic understanding of the embodiments. Thissummary is not an extensive overview of all contemplated embodiments andis not intended to identify key or critical elements of all embodimentsnor set limits on the scope of any or all embodiments. Its sole purposeis to present some concepts of one or more embodiments in a simplifiedform as a prelude to the more detailed description that is presentedlater.

According to one aspect, there is disclosed an apparatus installed on aplatform, the apparatus comprising a steering module that is configurednot only as described above, but is additionally configured (1) to haveaccess to the platform's orientation parameters, (2) to have access tothe platform's RCS parameters, (3) to have access to a detection thatone or more radar beams are impinging on the platform, (4) to haveaccess to either the location and radar parameters of the one or moreradars relative to the platform, or the beam patterns for the one ormore radars, (5) to have access to steering objectives that include thestandard comfort, safety, and navigation objectives and also radarsignature management objectives, and (6) to control the physical controlmechanisms so as to affect the platform's orientation parameters suchthat the observability of the platform is changed according to the radarsignature management objectives, which may have the objective ofincreasing the platform's observability to some radars, and reducing theplatform's observability to other radars according to some priorityand/or according to a radars' beam parameters or radar parameters orlocation.

According to another aspect, there is disclosed an apparatus provided ona platform, the apparatus comprising an error computing module and asteering module; wherein the error computing module is configured (1) tohave access to the platform's orientation parameters, (2) to have accessto the platform's RCS parameters, (3) to have access to a detection thatone or more radar beams are impinging on the platform, (4) to haveaccess to the locations and radar parameters for the one or more radars,or the beam parameters of the one or more radars, and (5) to compute andoutput an error-vector between (a) the platform's current orientationparameters, and (b) orientation parameters needed to make the AoA of aradar's signal equal to a preferred angle in the RCS parameters thatbetter meets the radar signature management objectives; and wherein thesteering module is configured (1) to have access to the platform'sorientation parameters, (2) to have access to steering objectives whichinclude reducing the magnitude of the error-vector, and (3) to controlthe physical control mechanism so as to affect the platform'sorientation parameters such that the combination of steering objectivesis satisfied and as such, the magnitude of the error-vector is reduced.According to another aspect, in these systems the radar's location andradar parameters may be provided by a direction finding (“DF”) system.

According to another aspect, in these systems access to the AoA of aradar's signal, frequency, and/or polarization, or to the radar'slocation, frequency, and/or polarization, may be provided by a directionfinding (“DF”) system. The DF system provide this information aftertracking the radar over a time duration. More than one DF systems may beused, and the data from the more than one DF systems may betriangulated. The DF system may be located on the platform.

According to another aspect, there is disclosed a system as describedabove wherein access to the radar's location, frequency, and/orpolarization, are provided by a steering module arranged to contain orreceive the radar cross section presented to an incoming radar beam as afunction of its (AoA), arranged to receive orientation, position, andvelocity vector of the platform and to cause platform controls to affectthe orientation of the platform based at least in part on the directionthe direction output to control a radar cross section presented to theincoming radar beam.

According to another aspect, there is disclosed an apparatus comprisinga radar direction finding module adapted to generate a direction outputsignal indicative of a direction of an origin of an incoming radar beamand a steering module arranged to receive the direction output signaland determine a future orientation based at least in part on thedirection of the origin of the incoming radar beam as indicated by thedirection output to control a radar cross section presented to theincoming radar beam.

According to another aspect, there is disclosed an aircraft, a radardirection finding module arranged on the aircraft and adapted togenerate a direction output signal indicative of a direction of anorigin of an incoming radar beam, and a steering module arranged toreceive the direction output signal and determine a future orientationbased at least in part on the direction of the origin of the incomingradar beam as indicated by the direction output to control a radar crosssection presented to the incoming radar beam.

According to another aspect, there is disclosed a method comprisinggenerating a direction output signal indicative of a direction of anorigin of an incoming radar beam and altering a future orientation ofthe aircraft based at least in part on the direction of the origin ofthe incoming radar beam as indicated by the direction output to controla radar cross section presented to the incoming radar beam.

According to another aspect, there is disclosed a method comprisingusing a radar direction finding module arranged on an aircraft togenerate a direction output signal indicative of a direction of anorigin of an incoming radar beam and using a steering module arranged onthe aircraft and to receive the direction output signal and adapted toalter a future orientation of the aircraft based at least in part on thedirection of the origin of the incoming radar beam as indicated by thedirection output to control a radar cross section presented to theincoming radar beam.

According to another aspect, there is disclosed an apparatus comprisinga radar direction finding module adapted to generate a direction outputsignal indicative of a direction of an origin of an incoming radar beamand a steering module arranged to receive the direction output signaland adapted to determine an orientation alteration based at least inpart on the direction of the origin of the incoming radar beam asindicated by the direction output to control a radar cross sectionpresented to the incoming radar beam. The steering module may be adaptedto determine an orientation alteration by altering at least one of yaw,pitch, and roll. The steering module may be adapted may be adapted todetermine an orientation alteration to instantaneously control a radarcross section presented to the origin of the incoming radar beam. Thesteering module may be adapted to determine an orientation alteration tocontrol a radar cross section presented to the origin of the incomingradar beam while traversing at least a portion of a future course.

According to another aspect, there is disclosed an apparatus comprisingan aircraft, a radar direction finding module arranged on the aircraftand adapted to generate a direction output signal indicative of adirection of an origin of an incoming radar beam, and a steering modulearranged to receive the direction output signal and adapted to determinean orientation alteration based at least in part on the direction of theorigin of the incoming radar beam as indicated by the direction outputto control a radar cross section presented to the incoming radar beam.The steering module may be adapted to alter a future orientation of theaircraft by altering at least one of pose, track, and altitude. Thesteering module may be adapted to determine an orientation alteration byaltering at least one of yaw, pitch, and roll. The steering module maycomprise an autopilot. The aircraft may comprise an unmanned aircraft.The steering module may be adapted to determine an orientationalteration by instantaneously controlling a radar cross section of theaircraft presented to the origin of the incoming radar beam. Thesteering module adapted to determine an orientation alteration bycontrolling a radar cross section of the aircraft presented to theorigin of the incoming radar beam while traversing at least a portion ofa future course. The aircraft may be adapted to aerobatic flight.

According to another aspect, there is disclosed a method comprisinggenerating a direction output signal indicative of a direction of anorigin of an incoming radar beam and altering a future orientation ofthe aircraft based at least in part on the direction of the origin ofthe incoming radar beam as indicated by the direction output to controla radar cross section presented to the incoming radar beam. Altering afuture orientation of the aircraft may comprise altering at least one ofyaw, pitch, and roll of the aircraft. Altering the future orientation ofthe aircraft may comprise instantaneously controlling a radar crosssection of the aircraft presented to the origin of the incoming radarbeam. Altering the future orientation of the aircraft may comprisecontrolling a radar cross section of the aircraft presented to theorigin of the incoming radar beam while traversing at least a portion ofa future course. The aircraft may comprise an unmanned aircraft. Theaircraft may be adapted to aerobatic flight and the future course of theaircraft may include one or more aerobatic maneuvers.

According to another aspect, there is disclosed a method comprisingusing a radar direction finding module arranged on an aircraft togenerate a direction output signal indicative of a direction of anorigin of an incoming radar beam, and using a steering module arrangedon the aircraft and to receive the direction output signal and adaptedto determine a future orientation of the aircraft based at least in parton the direction of the origin of the incoming radar beam as indicatedby the direction output to control a radar cross section presented tothe incoming radar beam. The future orientation may comprise altering atleast one of yaw, pitch, and roll of the aircraft. Altering the futureorientation of the aircraft may comprise instantaneously controlling aradar cross section of the aircraft presented to the origin of theincoming radar beam. Altering the future orientation of the aircraft maycomprise controlling a radar cross section of the aircraft presented tothe origin of the incoming radar beam while traversing at least aportion of a future course. The method may further comprise displayingthe altered future course of the aircraft. The steering module maycomprise an autopilot. The aircraft may comprise an unmanned aircraft.The aircraft may be adapted to aerobatic flight and changing theorientation of the aircraft may include one or more aerobatic maneuvers.

According to another aspect, there is disclosed an apparatus comprisinga radar detector adapted to detect at least two pulses of an incomingradar beam and to generate a radar detection signal indicative of thedetection and of characteristics of the detected pulses; a radardirection finding module arranged to receive the radar detection signaland adapted to generate a direction output signal indicative of adirection of an origin of an incoming radar beam, a radar estimatorarranged to receive the radar detection signal and adapted to generatean estimator output signal indicative of the pulse characteristics, anda steering module arranged to receive the direction output signal andthe estimator output signal and adapted to determine an orientationalteration based at least in part on the direction of the origin of theincoming radar beam as indicated by the direction output and theestimator output signal to control a radar cross section presented tothe incoming radar beam. The characteristics may include pulse signalstrength, timing of the pulses, and gaps in receiving the pulses. Thesteering module may comprise a memory storing information of the RCSversus azimuth for a platform carrying the apparatus. The steeringmodule may comprise a memory adapted to store information on constraintsin altering an orientation or course of a platform carrying theapparatus and wherein the steering module determines an orientationalteration based at least in part on the constraints. The constraintsmay include at least one of travel time between two way-points, arrivaltime at a point, and fuel remaining at a way-point. The apparatus mayfurther comprise a user interface arranged to enable a user to provideuser control signals and wherein the steering module may be arranged toreceive the user control signals and determines an orientationalteration based at least in part on the user control signals. The usercontrol signals may include at least one of decrease radar crosssection, increase radar cross section, and adjust orientation withoutregard to radar cross section. The apparatus may comprise user inputarranged to enable a user to provide user control signals and whereinthe steering module may be arranged to receive the user control signalsand determines an orientation alteration based at least in part on theuser control signals and the constraints. The user control signalsinclude at least one of decrease radar cross section, increase radarcross section, and determine orientation without regard to radar crosssection. The user control signals may include data on an amount ofweighting the steering module assigns to each of the constraints indetermining an orientation alteration. The radar detector and the radardirection finding module may be arranged on a first platform and thesteering module may be arranged on a second platform and the firstplatform may comprise a transmitter arranged to send information fromthe first platform to the second platform.

According to another aspect, there is disclosed an apparatus forregulating a radar signature of a platform, the apparatus comprising asteering module arranged to have access to data including: theplatform's orientation parameters; the platform's RCS parameters; one of(a) a location and radar parameters of at least one radar relative tothe platform and (b) beam parameters for at least one radar; andsteering objectives that include safety and navigation objectives andalso radar signature management objectives, and adapted to control atleast one physical control mechanism so as to affect the platform'sorientation parameters such that the observability of the platform maybe changed according to the radar signature management objectives.

According to another aspect, there is disclosed an apparatus forregulating a radar signature of a platform, the apparatus being locatedon the platform, the apparatus comprising an error computing modulearranged to have access to: the platform's orientation parameters; theplatform's RCS parameters; one of (a) a location and radar parametersfor at least one radar beam and (b) at least one beam parameter of atleast one radar beam, and adapted to compute and output an error-vectorbetween (a) the platform's current orientation parameters, and (b)orientation parameters needed to make an AoA of a radar's signal equalto an angle in the RCS parameters that better meets the radar signaturemanagement objectives and a steering module arranged to have access tothe platform's orientation parameters and steering objectives whichinclude reducing the magnitude of the error-vector, and adapted tocontrol the physical control mechanism so as to affect the platform'sorientation parameters such that the combination of steering objectivesmay be satisfied and as such, the magnitude of the error-vector may bereduced. The apparatus may further comprise a direction finding systemand wherein the one of (a) the location and radar parameters for atleast one radar beam and (b) at least one beam parameter of at least oneradar beam, are provided by the DF system. The apparatus may furthercomprise a direction finding system adapted to provide information inthe form of one of (a) the radar signal's AoA, frequency, orpolarization, and (b) the radar's location, frequency, or polarization,to the error computing module. The direction finding systems may beadapted to perform tracking of the at least one radar beam over a timeduration and to provide the information at least partially on the basisof the tracking. The apparatus may comprise at least two additionaldirection finding systems located on other platforms and wherein theerror computing module triangulates the data from the at least threedirection finding systems to determine the radar location relative tothe platform. A access to the at least one radar beams location,frequency, or polarization may be provided by the steering module, thesteering module being arranged to contain or receive the radar crosssection presented to an incoming radar beam as a function of its AoA,arranged to receive orientation, position, and velocity vector of theplatform and to cause platform controls to affect the orientation of theplatform based at least in part on the direction the direction output tocontrol a radar cross section presented to the incoming at least oneradar beam.

Further embodiments, features, and advantages of the present invention,as well as the structure and operation of the various embodiments aredescribed in detail below with reference to accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example of aircraft visibility as afunction of azimuth.

FIG. 2 is a diagram showing an example of radar cross section as afunction of azimuth.

FIG. 3 is a functional block diagram of a system according to an aspectof an embodiment of the present invention.

FIG. 4 is a flowchart showing a method according to an aspect of anembodiment of the present invention.

FIG. 5 is a flowchart showing a method according to another aspect of anembodiment of the present invention.

FIG. 6 is a flowchart showing a method according to another aspect of anembodiment of the present invention.

FIG. 7 is a diagrammatic representation of distribution of functionalityaccording to another aspect of an embodiment of the present invention.

FIG. 8A is a diagrammatic representation of distribution offunctionality according to another aspect of an embodiment of thepresent invention.

FIG. 8B is a diagrammatic representation of distribution offunctionality according to another aspect of an embodiment of thepresent invention.

Further features and advantages of the invention, as well as thestructure and operation of various embodiments of the invention, aredescribed in detail below with reference to the accompanying drawings.It is noted that the invention is not limited to the specificembodiments described herein. Such embodiments are presented herein forillustrative purposes only. Additional embodiments will be apparent topersons skilled in the relevant art based on the teachings containedherein.

DETAILED DESCRIPTION

Various embodiments are now described with reference to the drawings,wherein like reference numerals are used to refer to like elementsthroughout. In the following description, for purposes of explanation,numerous specific details are set forth in order to promote a thoroughunderstanding of one or more embodiments. It may be evident in some orall instances, however, that any embodiment described below can bepracticed without adopting the specific design details described below.In other instances, well-known structures and devices are shown in blockdiagram form in order to facilitate description of one or moreembodiments.

Embodiments of the invention may be implemented in hardware, firmware,software, or any combination thereof. Embodiments of the invention mayalso be implemented as instructions stored on a machine-readable medium,which may be read and executed by one or more processors. Amachine-readable medium may include any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputing device). For example, a machine-readable medium may includesolid state memory, read only memory (ROM), random access memory (RAM),magnetic disk storage media, optical storage media, flash memorydevices; electrical, optical, acoustical or other forms of propagatedsignals (e.g., carrier waves, infrared signals, digital signals, etc.),and others. Further, firmware, software, routines, and instructions maybe described herein as performing certain actions. However, it should beappreciated that such descriptions are merely for convenience and thatsuch actions in fact result from computing devices, processors,controllers, or other devices executing the firmware, software,routines, instructions, etc.

With initial reference to FIG. 1 there is shown as an example of aplatform an aircraft 10 in flight. Generally speaking, the aircraft 10will have varying amounts of visibility to a radar beam impinging on theaircraft in the plane of the figure depending on the azimuthal angle.For example, the amount of visibility may be at a minimum directly aheadof the aircraft 10 as indicated by the sector 20. The visibility maygenerally increase as a function of angular deviance from the directionof travel as indicated by sectors 30 and 40 and may further increase asindicated by sector 50. These principles are further illustrated in FIG.2. The amplitude of the return signal expressed in terms of the radarcross section, a, in dB square meters (dBm²) may vary as a function ofazimuth as shown.

RF emitters include conventional radar, e.g. active and monostatic(meaning emitter and receiver are co-located) and passive radar thatuses emitters of opportunity (e.g. broadcast AM, FM and TV) to with apassive radar receiver (bistatic) to detect and track aircraft. Theterms radar, RF radar, and RF emitter are intended to encompass all suchsystems.

Various systems and methods for determining the direction of an incomingradar beam are known in the art. For example, U.S. Pat. No. 9,880,260 toMcCorkle, titled “Electrically Small, Range And Angle-of-Arrival RFSensor and Estimation System” issued Jan. 30, 2018 (McCorkle '260) andassigned to the assignee of the present application, the entirespecification of which is hereby incorporated by reference, discloses anRF emitter sensing device having an antenna circuit and an estimatorconfigured to output, for one or more incoming signals-of-interest(SoI), either or both of an estimated range to the emitter of each SoI,and estimates for one or more angles corresponding to the 3Dangle-of-arrival (AoA) for each SoI. This is one such system fordirection finding, one of ordinary skill in the art will be familiarwith other suitable direction-finding systems as well.

A platform such as an aircraft provided with the ability to detect thedirection of an incoming radar beam may use this information to alterits orientation so as to control the radar cross section which theplatform is presenting to the beam. This control may be immediate, thatis, the aircraft can make an immediate change in orientation to alterits radar cross section. Alternatively, or in addition, the aircraft mayalter all or portions of its longer term orientation over the course ofits travel so as to control its radar cross section as much as possiblewhile also satisfying other constraints on its ability to alter itsorientation, such as transit time. In other words, the aircraft'sability to alter its orientation to reduce its radar cross section maybe constrained by other variables such as desired arrival time, amountof fuel, and so on. In general, a system may be devised which takes allof these parameters into account and supplies the best overallorientation. Optimization of multiple objectives is commonly done,including items such as navigation, passenger comfort, and G-forcelimits.

For some applications, it may be beneficial that the aircraft beprovided with the optimizations to perform aerobatic maneuvers such asskids, slips etc. so that it may alter orientation quickly. Theprinciples described here may be used to assist pilot control ofexisting aircraft. The principles described herein may be used withflight controls for more instantaneous response to radar angle ofarrival.

The following discussion is in terms of an aircraft. This broadlyencompasses all forms of aircraft including unmanned aircraft. It willbe apparent, however, that the principles may be applied to otherplatforms.

As used herein, the direction of a radar beam means the direction ofpropagation of the beam from its source to the platform. It should benoted that in addition to presenting a controlled, e.g., minimum crosssection, it may also be useful to limit detection by Doppler radar bytraveling along a course which is as orthogonal to the beam as possiblein view of other constraints.

The term “heading” (yaw) is used herein in its conventional sense asdescribing the direction a platform is pointing. The term “course” or“course angle” refers to the direction a platform is actually moving.The terms “orientation” or “pose” (roll, pitch and yaw) are usedinterchangeably to describe an orientation with respect to an incomingradar beam. Thus, there are multiple orientations that deliver the samecourse.

RCS defines the magnitude of the radar return as a function offrequency, azimuth, elevation and polarization. According to an aspectof an embodiment, radar returns are controlled by varying the platformorientation with respect to the radar beam. One example is altering theaircraft's orientation to present an RCS null to the radar for thefrequency and polarization the radar has been determined to be using.

Doppler is indicative of the rate a platform is moving toward or awayfrom the radar. It is used to separate fast moving targets from clutter(e.g. radar returns from trees, buildings, terrain) that are slowmoving. The Doppler return can be controlled by altering course. Oneexample is turning course perpendicular to the radar beam, which wouldresult in zero Doppler. The aircraft would end up circling the radar. Ifthe aircraft were low to the ground, and there was a lot of clutter, theaircraft would effectively “disappear to the clutter.”

For fixed wing aircraft, the x-axis is taken as positive from the tailto through the nose of the aircraft. The aircraft nose can rotate up anddown about the y-axis, a motion known as pitch. Pitch control istypically accomplished using an elevator on the horizontal tail. Second,the wingtips can rotate up and down about the x-axis, a motion known asroll. Roll control is usually provided using ailerons located at eachwingtip. Finally, the nose can rotate left and right about the z-axis, amotion known as yaw. Yaw control is most often accomplished using arudder located on the vertical tail. These can change the angle to theradar without (necessarily) impacting direction of flight. In thedescription that follows, the signals generated in response to a radarcontact are used to influence the positions of these control surfaces.

Some of the discussion which follows is in terms of various modules orsystems for performing certain functions. Although shown in the figuresand described as co-located, it will be understood by one of ordinaryskill in the art that these modules maybe may be distributed between oramong multiple platforms as explained in more detail below.

Turning now to FIG. 3, there is depicted a functional block diagram of adirection-finding based radar signature management system 100 accordingto one aspect of an embodiment. A radar beam 110 propagates as shown bythe open arrow. A direction finding module 120 detects the incomingradar beam 110 and determines the direction from which the radar beam110 is coming. Direction finding module 120 produces a signal 130 whichis indicative of the direction of the incoming radar beam 110.Additionally, it can produce signals indicative of the radar beam'sfrequency, polarization and waveform and time pulse repetitioncharacteristics. Signal 130 is presented to a steering module 140. Thesteering module 140 produces a signal 150 which indicates an alterationto an existing orientation or course to manage (e.g., reduce or enhance)the radar signature of the aircraft.

For some applications it is advantageous to provide the steering modulewith the ability to manage multiple constraints in determining a changein orientation or course. In other words, in general there may becircumstances in which simply adopting an orientation that minimizes RCSwould be impractical due to other constraints such as travel timebetween two way-points, or arrival time at a point, or on fuel remainingat a way-point. In such circumstances, in some embodiments the steeringmodule is able to determine the optimal change in orientation that canbe effected without unduly compromising the ability to satisfy theseother constraints. Conversely there may be circumstances in which it isknown that the platform is subject to only low detectability. In suchcircumstances satisfying the other constraints can have a higher weightor priority. It may even be desired to maximize RCS in low detectabilityconditions. In the embodiment of FIG. 3 an interface 145 provides anability to control the steering module 140 to cause it, for example, tooperate in a mode in which it seeks to minimize the radar signature, oroperate in a mode in which it seeks to maximize the radar signature, ordisengage control of radar signature entirely, that is, operate withoutregard to effect on radar signature. Through the interface weighting canbe assigned to the other objectives or constraints such as thosedescribed above.

FIG. 4 is a functional block diagram of a method to be implementedaccording to another aspect of an embodiment. In a step S10 the incomingradar signal is detected. In a step S20 the direction of the incomingradar signal is determined. Frequency, polarization, waveform and pulserepetition timing (intervals may be at variable times, so notnecessarily a rate or frequency) may be determined as well. In a stepS30 an orientation alteration is determined based at least in part onthe direction determination made in step S20. In step S40 the aircraftis caused to fly according to the orientation as altered by theorientation alteration determination made in step S30.

FIG. 5 is a functional block diagram of a method to be implementedaccording to another aspect of an embodiment. In a step S50 the aircraftflies according to its existing orientation. In step S60 a determinationis made of whether radar has been detected. If no radar has beendetected in step S60, then the aircraft continues to fly its normalorientation. If radar is detected, however, then in step S70 adetermination is made of the direction of the incoming radar signal.Then, in a step S80, a determination is made of what orientationalteration should be imposed. In step S90 the aircraft is made to flyaccording to the altered orientation. In step S100 a determination ismade whether the radar is still present. If the radiator is no longerpresent, then the process reverts to step S50 and the aircraft revertsto flying its originally intended orientation, that is, without furthermaneuvers to avoid radar. If the radar is still present, then theprocess may revert to step S80 and a new orientation alteration may bedetermined. Alternatively, the process can revert to step S90 where theaircraft continues to fly according to the previous orientationalteration.

FIG. 6 is a flowchart describing a method according to another aspect ofan embodiment. In FIG. 6, is a step S200 the RF radar signal isacquired. This can be accomplished, for example, using an antenna of thetype described in McCorkle '260 incorporated above. It will be apparent,however, that other antennas and devices for acquiring the signal may beused. In step S210 parameters of the acquired signal such as its anglesof arrival, frequency, and polarization are determined. In step S220 theorientation to control the RCS presented to the radar signal origin isdetermined. Also, at the same time, if it is desired to control theDoppler signal returned by the aircraft then the course to control theDoppler return signal is also determined. In step S230 it is determinedhow to set the aircraft actuators to achieve the orientation (and courseif desired) determined in step S220. In step 240 the control surfacesare adjusted as determined in step S230. For aircraft other than fixedwing aircraft such as multi-rotor-copters and helicopters theorientation and course can be adjusted in a known manner.

Hardware and software systems to provide the functionality describedabove can all be located on a single platform such as an aircraft. FIG.7 graphically depicts an arrangement in which a platform 705, which may,for example, be an aircraft, is provided with a radar acquisition module710 which acquires the RF radar signal. As noted, this radar acquisitionmodule 710 may be implemented as described in McCorkle '260 or maybesome other suitable system. The radar acquisition module 710 providesinformation about the acquired signal to a detection, classification,and direction finding module 720. Detection, classification, anddirection finding module 720 then generates a signal conveying thedirection finding data, the angle of arrival of the RF radar signal, andthe frequency of the RF radar signal to an RCS and Doppler controlmodule 770 which determines what changes to orientation and coursesettings are desired and supplies those signals to an RCS and Doppleraugmented autopilot module 780 which generates the control signals forthe control surfaces of an aircraft. For some applications, it may alsobe advantageous if RCS and Doppler control module 770 also takes intoaccount geographic information such as the position of platform 700 andterrain between radar and aircraft. The system shown in FIG. 7 may alsoinclude an interface 145 as described above.

The systems and methods disclosed herein for some applicationsadvantageously employ a radar estimator 775. In general terms, someradars are mechanically rotated, and some are not. Phased array versionscan blink and randomize pulse times. Mechanically rotated radar canleave a gap of several seconds between the times when several pulses hitthe aircraft. A radar-state estimator, or simply radar estimator, is asystem that examines the pulse detections, their signal strength, andthe timing and gaps in receiving them. It may be a separate component asshown or may be incorporated into another component such as the RCS andDoppler control module 770 which can use this information to tell thesteering module algorithms when to coast, and when the aircraft couldturn through high RCS angles and get to another low RCS angle before theradar beam comes back to paint the aircraft again.

For some applications and implementations, it may be advantageous tostore and use data pertaining to the aircraft RCS in a memory 777 whichmay be part of the RCS and Doppler control module 770 as shown orlocated elsewhere. Aircraft RCS is generally a multidimensional functionof factors such as frequency of the RF radar signal, aircraft azimuthalangle and elevation angle with respect to the radar beam, andpolarization of the radar beam. A matrix of RCS azimuth and elevationvalues for each frequency and polarization (e.g. vertical, horizontal,circular . . . ) can be stored. Alternatively, RCS azimuth and elevationvalues can be computed by functions (e.g. curve fitting) or acombination of stored and computed, as in an interpolator.

Alternatively, these systems may be distributed among multipleplatforms. FIG. 8A graphically depicts an arrangement in which a firstplatform 700, which may, for example, be an aircraft, is provided withthe components necessary to provide the front-end functionality ofacquiring the RF signal and detecting, classifying, and determining adirection of that signal. More specifically, a radar acquisition module710 acquires the signal. As noted, this radar acquisition module 710 maybe implemented as described in McCorkle '260 or maybe some othersuitable system. The radar acquisition module 710 provides informationabout the acquired signal to a detection, classification, and directionfinding module 720. Detection, classification, and direction findingmodule 720 then generates a signal 730 carrying the direction findingdata, the angle of arrival of the RF radar signal, and the frequency ofthe RF radar signal. For some applications, it may also be advantageousif platform 700 also provides geographic information such as theposition of platform 700 and may include a radar estimator as describedabove. This information is conveyed as the signal 730 to an informationdistribution system depicted as cloud 740, which may be a direct radiolink, or may be a link through a system of servers, or any other systemthat can relay the information from platform 700 as a signal 750. Thesignal 750 is received by a second platform 760 which may, for example,be a second aircraft. Platform 760 includes an RCS and Doppler controlmodule 770 which determines what changes to orientation and coursesettings are desired and supplies those signals to an RCS and Doppleraugmented autopilot module 780 which generates the control signals forthe control surfaces of an aircraft.

FIG. 8B also graphically depicts an arrangement in which a firstplatform 700, which may, for example, be an aircraft, is provided withthe components necessary to provide the front-end functionality ofacquiring the RF signal and detecting, classifying, and determining adirection of that signal. More specifically, a radar acquisition module710 acquires the RF radar signal. As noted, this radar acquisitionmodule 710 may be implemented as described in McCorkle '260 or maybesome other suitable system. The radar acquisition module 710 providesinformation about the acquired signal to a detection, classification,and direction finding module 720. Detection, classification, anddirection finding module 720 then generates a signal 730 carrying thedirection finding data, the angle of arrival of the RF radar signal, andthe frequency of the RF radar signal. For some applications, it may alsobe advantageous if platform 700 also provides geographic informationsuch as the position of platform 700 and may include a radar estimatoras described above. This information is conveyed as the signal 730 to aninformation distribution system depicted as cloud 740, which may be adirect radio link, or may be a link through a system of servers, or anyother system that can relay the information from platform 700 as asignal 750. The signal 750 is received by a second platform 800 whichmay, for example, be a second aircraft or ground based. Platform 810which in the example is an aircraft sends to the cloud 740 a signal 820,received by platform 800 as signal 820 which conveys information on thepresent orientation state N and present course state N of the platform810. Platform 800 includes an RCS and Doppler control module 770 whichdetermines based on the information conveyed in signal 740 and 830 whatchanges to orientation and course settings are desired and suppliesthose signals as signals 840, 850 as new orientation N+1 and new courseN+1 through cloud 740 as a signal 850 to an RCS and Doppler augmentedautopilot module 780 on platform 810 which generates the control signalsfor the control surfaces of platform 810.

The above description includes examples of one or more embodiments. Itis, of course, not possible to describe every conceivable combination ofcomponents or methodologies for purposes of describing theaforementioned embodiments, but one of ordinary skill in the art mayrecognize that many further combinations and permutations of variousembodiments are possible. Accordingly, the described embodiments areintended to embrace all such alterations, modifications and variationsthat fall within the spirit and scope of the appended claims.Furthermore, to the extent that the term “includes” is used in eitherthe detailed description or the claims, such term is intended to beinclusive in a manner similar to the term “comprising” as “comprising”is construed when employed as a transitional word in a claim.Furthermore, although elements of the described aspects and/orembodiments may be described or claimed in the singular, the plural iscontemplated unless limitation to the singular is explicitly stated.Additionally, all or a portion of any aspect and/or embodiment may beutilized with all or a portion of any other aspect and/or embodiment,unless stated otherwise.

What is claimed is:
 1. Apparatus comprising: a radar direction finding module adapted to generate a direction output signal indicative of a direction of an origin of an incoming radar beam; and a steering module arranged to receive the direction output signal and adapted to determine an orientation alteration based at least in part on the direction of the origin of the incoming radar beam as indicated by the direction output to control a radar cross section presented to the incoming radar beam.
 2. Apparatus as claimed in claim 1 wherein the steering module is adapted to determine an orientation alteration by altering at least one of yaw, pitch, and roll.
 3. Apparatus as claimed in claim 1 wherein the steering module is adapted to determine an orientation alteration to instantaneously control a radar cross section presented to the origin of the incoming radar beam.
 4. Apparatus as claimed in claim 1 wherein the steering module is adapted to determine an orientation alteration to control a radar cross section presented to the origin of the incoming radar beam while traversing at least a portion of a future course.
 5. Apparatus comprising: an aircraft; a radar direction finding module arranged on the aircraft and adapted to generate a direction output signal indicative of a direction of an origin of an incoming radar beam; and a steering module arranged to receive the direction output signal and adapted to determine an orientation alteration based at least in part on the direction of the origin of the incoming radar beam as indicated by the direction output to control a radar cross section presented to the incoming radar beam.
 6. Apparatus as claimed in claim 5 wherein the steering module is adapted to alter a future orientation of the aircraft by altering at least one of pose, track, and altitude
 7. Apparatus as claimed in claim 5 wherein the steering module is adapted to determine an orientation alteration by altering at least one of yaw, pitch, and roll.
 8. Apparatus as claimed in claim 5 wherein the steering module comprises an autopilot.
 9. Apparatus as claimed in claim 5 wherein the aircraft comprises an unmanned aircraft.
 10. Apparatus as claimed in claim 5 wherein the steering module is adapted to determine an orientation alteration by instantaneously controlling a radar cross section of the aircraft presented to the origin of the incoming radar beam.
 11. Apparatus as claimed in claim 5 wherein the steering module is adapted to determine an orientation alteration by controlling a radar cross section of the aircraft presented to the origin of the incoming radar beam while traversing at least a portion of a future course.
 12. Apparatus as claimed in claim 5 wherein the aircraft is adapted to aerobatic flight.
 13. A method comprising: generating a direction output signal indicative of a direction of an origin of an incoming radar beam; and altering a future orientation of the aircraft based at least in part on the direction of the origin of the incoming radar beam as indicated by the direction output to control a radar cross section presented to the incoming radar beam.
 14. A method as claimed in claim 13 wherein altering a future orientation of the aircraft comprises altering at least one of yaw, pitch, and roll of the aircraft.
 15. A method as claimed in claim 13 wherein altering the future orientation of the aircraft comprises instantaneously controlling a radar cross section of the aircraft presented to the origin of the incoming radar beam.
 16. A method as claimed in claim 13 wherein the altering the future orientation of the aircraft comprises controlling a radar cross section of the aircraft presented to the origin of the incoming radar beam while traversing at least a portion of a future course.
 17. A method as claimed in claim 13 wherein the aircraft comprises an unmanned aircraft.
 18. A method as claimed in claim 13 wherein the aircraft is adapted to aerobatic flight and the future course of the aircraft includes one or more aerobatic maneuvers.
 19. A method comprising: using a radar direction finding module arranged on an aircraft to generate a direction output signal indicative of a direction of an origin of an incoming radar beam; and using a steering module arranged on the aircraft and to receive the direction output signal and adapted to determine a future orientation of the aircraft based at least in part on the direction of the origin of the incoming radar beam as indicated by the direction output to control a radar cross section presented to the incoming radar beam.
 20. A method as claimed in claim 19 wherein altering a future orientation comprises altering at least one of yaw, pitch, and roll of the aircraft.
 21. A method as claimed in claim 19 wherein altering the future orientation of the aircraft comprises instantaneously controlling a radar cross section of the aircraft presented to the origin of the incoming radar beam.
 22. A method as claimed in claim 19 wherein the altering the future orientation of the aircraft comprises controlling a radar cross section of the aircraft presented to the origin of the incoming radar beam while traversing at least a portion of a future course.
 23. A method as claimed in claim 19 further comprising displaying the altered future course of the aircraft.
 24. A method as claimed in claim 19 wherein the steering module comprises an autopilot.
 25. A method as claimed in claim 19 wherein the aircraft comprises an unmanned aircraft.
 26. A method as claimed in claim 19 wherein the aircraft is adapted to aerobatic flight and changing the orientation of the aircraft includes one or more aerobatic maneuvers.
 27. Apparatus comprising: a radar detector adapted to detect at least two pulses of an incoming radar beam and to generate a radar detection signal indicative of the detection and of characteristics of the detected pulses; a radar direction finding module arranged to receive the radar detection signal and adapted to generate a direction output signal indicative of a direction of an origin of an incoming radar beam; a radar estimator arranged to receive the radar detection signal and adapted to generate an estimator output signal indicative of the pulse characteristics; and a steering module arranged to receive the direction output signal and the estimator output signal and adapted to determine an orientation alteration based at least in part on the direction of the origin of the incoming radar beam as indicated by the direction output and the estimator output signal to control a radar cross section presented to the incoming radar beam.
 28. Apparatus as claimed in claim 27 wherein the characteristics include pulse signal strength, timing of the pulses, and gaps in receiving the pulses.
 29. Apparatus as claimed in claim 27 wherein the steering module comprises a memory storing information of the RCS versus azimuth for a platform carrying the apparatus.
 30. Apparatus as claimed in claim 27 wherein the steering module comprises a memory adapted to store information on constraints in altering an orientation or course of a platform carrying the apparatus and wherein the steering module determines an orientation alteration based at least in part on the constraints.
 31. Apparatus as claimed in claim 30 wherein the constraints include at least one of travel time between two way-points, arrival time at a point, and fuel remaining at a way-point.
 32. Apparatus as claimed in claim 27 further comprising a user interface arranged to enable a user to provide user control signals and wherein the steering module is arranged to receive the user control signals and determines an orientation alteration based at least in part on the user control signals.
 33. Apparatus as claimed in claim 32 wherein the user control signals include at least one of decrease radar cross section, increase radar cross section, and adjust orientation without regard to radar cross section.
 34. Apparatus as claimed in claim 30 further comprising a user interface arranged to enable a user to provide user control signals and wherein the steering module is arranged to receive the user control signals and determines an orientation alteration based at least in part on the user control signals and the constraints.
 35. Apparatus as claimed in claim 34 wherein the user control signals include at least one of decrease radar cross section, increase radar cross section, and determine orientation without regard to radar cross section.
 36. Apparatus as claimed in claim 35 wherein the user control signals include data on an amount of weighting the steering module assigns to each of the constraints in determining an orientation alteration.
 37. Apparatus as claimed in claim 30 wherein the radar detector and the radar direction finding module are arranged on a first platform and the steering module is arranged on a second platform and wherein the first platform comprises a transmitter arranged to send information from the first platform to the second platform.
 38. Apparatus for regulating a radar signature of a platform, the apparatus comprising: a steering module arranged to have access to data including: the platform's orientation parameters; the platform's RCS parameters; one of (a) a location and radar parameters of at least one radar relative to the platform and (b) beam parameters for at least one radar; and steering objectives that include safety and navigation objectives and also radar signature management objectives, and adapted to control at least one physical control mechanism so as to affect the platform's orientation parameters such that the observability of the platform is changed according to the radar signature management objectives.
 39. Apparatus for regulating a radar signature of a platform, the apparatus being located on the platform, the apparatus comprising: an error computing module arranged to have access to: the platform's orientation parameters; the platform's RCS parameters; one of (a) a location and radar parameters for at least one radar beam and (b) at least one beam parameter of at least one radar beam, and adapted to compute and output an error-vector between (a) the platform's current orientation parameters, and (b) orientation parameters needed to make an AoA of a radar's signal equal to an angle in the RCS parameters that better meets the radar signature management objectives; and a steering module arranged to have access to the platform's orientation parameters and steering objectives which include reducing the magnitude of the error-vector, and adapted to control the physical control mechanism so as to affect the platform's orientation parameters such that the combination of steering objectives is satisfied and as such, the magnitude of the error-vector is reduced.
 40. Apparatus as claimed in claim 39 further comprising a direction finding system and wherein the one of (a) the location and radar parameters for at least one radar beam and (b) at least one beam parameter of at least one radar beam, are provided by the DF system.
 41. Apparatus as claimed in claim 39 further comprising a direction finding system adapted to provide information in the form of one of (a) the radar signal's AoA, frequency, or polarization, and (b) the radar's location, frequency, or polarization, to the error computing module.
 42. Apparatus as claimed in claim 41 wherein the direction finding system is adapted to perform tracking of the at least one radar beam over a time duration and to provide the information at least partially on the basis of the tracking.
 43. Apparatus as claimed in claim 40 comprising at least two additional direction finding systems located on other platforms and wherein the error computing module triangulates the data from the at least three direction finding systems to determine the radar location relative to the platform.
 44. Apparatus as claimed in claim 40 wherein access to the at least one radar beam's location, frequency, or polarization is provided by the steering module, the steering module being arranged to contain or receive the radar cross section presented to an incoming radar beam as a function of its AoA, arranged to receive orientation, position, and velocity vector of the platform and to cause platform controls to affect the orientation of the platform based at least in part on the direction the direction output to control a radar cross section presented to the incoming at least one radar beam. 